1. Field of the Invention
The present invention relates to a thermal oxide film structure on an upper surface of a guard ring formation region in a semiconductor device, more particularly to an element for reducing effects of moving ions.
2. Description of the Related Art
In a conventional semiconductor device, for example, an insulated gate bipolar transistor, a guard ring part (region B) is formed to be continuous with a unit cell part (region A) of an IGBT element in a peripheral region of an element forming region. Accordingly, there has been known an element structure which improves withstand voltage of a guard ring without increasing an ON-resistance of the element (for example, see patent document 1).
Moreover, in a conventional semiconductor integrated circuit, for example, an integrated circuit for high power applications, a P-type guard ring layer is formed in a peripheral part of a vertical IGBT. On the guard ring layer, a horizontal device such as a diode is disposed with an insulating layer interposed therebetween. Accordingly, there has been known an element structure capable of preventing an intensive electric field by equalizing distribution of equal potential lines in both of the vertical IGBT and the horizontal device.
[Patent Document 1]
U.S. Pat. No. 2,950,025 (Page 3 and Page 4, FIG. 1 to FIG. 3)
[Patent Document 2]
Japanese Patent Laid-Open No. Hei 10 (1998)-256542 (Page 3 and Page 4, FIG. 1 to FIG. 3)